Abstract: This study provides a better knowledge of key parameters controlling the mobility of Dissolved Organic Carbon (DOC), As, Cd, Cr, Cu, Ni, Pb and Zn from contaminated marine sediment in contact with acidified seawater using static and dynamic standard leaching tests. These procedures have been modified in order to use different leaching agents, L/S ratios, contact times and pH values that simulate seawater acidification under CO2 leakages scenarios. Studied sediment from a potential area of CO2 storage, shows a high acid neutralisation capacity (ANC pH = 4 = 3.58 eq/kg) for deionised water as well as for seawater (ANC pH = 4 = 3.97 eq/kg). The availability control mechanism is shown by releasing Cd with seawater at pH values 6, 7 and 8 and by the releasing of Zn with seawater at pH 6; the solubility control mechanism appears for Ni release using natural seawater. Experimental results of metal release from the pH dependence leaching test are modelled with Visual MINTEQ geochemical software to predict metal release from sediment, obtaining minor differences with experimental values. An improvement in the metal release results has been obtained considering in the model the influence of the DOC, Fe- and Al-(hydr)oxides, humic acids and fulvic acids. The obtained results would be useful as a line of evidence input for the risk assessment of a Carbon Capture and Storage site where acidified seawater at different concentrations of CO2 is in contact with sediment.

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